Enhanced Ignition in Inductively Coupled Plasmas For Workpiece Processing

ABSTRACT

Plasma processing apparatus and associated methods are provided. In one example, a plasma processing apparatus includes a plasma chamber. The plasma processing apparatus includes a dielectric wall forming at least a portion of the plasma chamber. The plasma processing apparatus includes an inductive coupling element located proximate the dielectric wall. The plasma processing apparatus includes an ultraviolet light source configured to emit an ultraviolet light beam onto a metal surface that faces an interior volume of the plasma chamber. The plasma processing apparatus includes a controller configured to control the ultraviolet light source.

PRIORITY CLAIM

The present application claims priority to and is a continuation in partapplication of U.S. application Ser. No. 16/537,748, titled “EnhancedIgnition in Inductively Coupled Plasmas for Workpiece Processing,” filedon Aug. 12, 2019, which is incorporated herein by reference.

FIELD

The present disclosure relates generally to plasma processing using aplasma source.

BACKGROUND

Plasma processing tools can be used in the manufacture of devices suchas integrated circuits, micromechanical devices, flat panel displays,and other devices. Plasma processing tools used in modern plasma etchapplications are required to provide a high plasma uniformity and aplurality of plasma controls, including independent plasma profile,plasma density, and ion energy controls. Plasma processing tools can, insome cases, be required to sustain a stable plasma in a variety ofprocess gases and under a variety of different conditions (e.g., gasflow, gas pressure, etc.).

SUMMARY

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

One example aspect of the present disclosure is directed to a plasmaprocessing apparatus. The plasma processing apparatus includes a plasmachamber. The plasma processing apparatus includes a dielectric wallforming at least a portion of the plasma chamber. The plasma processingapparatus includes an inductive coupling element located proximate thedielectric wall. The plasma processing apparatus includes an ultravioletlight source configured to emit an ultraviolet light beam onto a metalsurface that faces an interior volume of the plasma chamber. The plasmaprocessing apparatus includes a controller configured to control theultraviolet light source.

Variations and modifications can be made to example embodiments of thepresent disclosure.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure to one of ordinary skill in the art isset forth more particularly in the remainder of the specification,including reference to the accompanying figures, in which:

FIG. 1 depicts an example plasma processing apparatus according toexample embodiments of the present disclosure;

FIG. 2 depicts a flow diagram of an example method according to exampleembodiments of the present disclosure;

FIG. 3 depicts an example plasma processing apparatus according toexample embodiments of the present disclosure;

FIG. 4 depicts an example plasma processing apparatus according toexample embodiments of the present disclosure;

FIG. 5 depicts an example plasma processing apparatus according toexample embodiments of the present disclosure; and

FIG. 6 depicts an example plasma processing apparatus according toexample embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Example aspects of the present disclosure are directed to plasmaprocessing apparatus and associated methods for enhancing ignition ofinductively coupled plasmas, and in some embodiments electrostaticallyshielded inductively coupled plasmas. Ignition of inductively coupledplasma (also referred to as inductively coupled plasma striking) can beimproved with an ultraviolet light source that emits an ultravioletlight beam onto a dielectric wall and/or a metal surface at a locationproximate the plasma prior to or during ignition of the plasma (e.g.,from a location outside of the plasma chamber). As such, less RF powercan be used to ignite (also referred to as strike) the plasma in lesstime, with better igniting repeatability and reducing ion bombardment ofa dielectric window.

In some example plasma sources, inductive plasma sources with reducedcapacitive coupling (e.g., due to electrostatic shielding) can havesubstantial advantages over other inductive sources that are common insemiconductor processing. Such plasma sources with reduced capacitivecoupling can have: (1) reduced ion bombardment and sputtering ofinterior dielectric and metal walls of the plasma source; (2) reducedplasma potential and improved ion optics for extraction; (3) increasedlifetime of source components and improved cleanliness due to reducedwear and roughening of inner surfaces. Conventional plasma sources withreduced capacitive coupling (due to electrostatic shielding, RFfrequency or coil configuration) can have intermittent and/or slowignition of the plasma due to a reduced electric field in a plasmachamber (also referred to as a plasma vessel). Conventional plasmasources can use much higher radio frequency (RF) power and coil voltageto achieve reliable plasma ignition, particularly when higher gaspressures such as above about 500 mTorr are used. However, higher RFpower, higher coil voltage and/or higher gas pressures cannot alwaysyield reliable ignition, and can often have detrimental side effectssuch as arcing and localized sputtering of dielectric walls.

In some example plasma sources, a smaller supplemental electrode can beused in a processing chamber of a conventional plasma processingapparatus providing RF power until ignition is achieved. However, suchignition approaches can cause sputtering of the electrode or walladjacent the electrode resulting in contamination and/or surfaceroughening that can lead to particle contamination.

According to example aspects of the present disclosure, an ultravioletlight source can be operated to illuminate an inner wall of a plasmachamber such that a larger number (e.g., greater than about 10⁴) of freeelectrons can be ejected from the illuminated wall into a gas in theplasma chamber to substantially enhance a rate of initial exponentialgrowth of the plasma with the substantially inductive coupling of theplasma source. The ultraviolet light source can be used to reduce andmake more consistent ignition time of the plasma, even at reduced RFpower levels. Thus, for inductively coupled plasma sources (e.g.,induction coil or antenna) with reduced capacitive coupling (e.g. due topresence of electrostatic shield or other feature), ignition enhancementcan be provided using an ultraviolet light source in a plasma chamber.

In some embodiments, one or more ultraviolet light sources (e.g., a lampor lamps) can be mounted external to a plasma chamber for an inductivelycoupled plasma source such that the radiation from the ultraviolet lightsource(s) can illuminate an inner wall (e.g., dielectric wall and/ormetal wall) of the plasma chamber. The wall can have direct line ofsight to the plasma chamber. For instance, there are no structuresblocking a path (e.g., line of sight path) between the wall and aninterior of the plasma chamber where the plasma is generated.

The ultraviolet light source(s) can have substantial portion of itsoutput (e.g., ultraviolet light beam) as electromagnetic radiation (EM)radiation below about 250 nanometers (nm) wavelength, down to about 100nm wavelength.

In some embodiments, an electrostatic shield can be located between adielectric wall, which forms at least a portion of the plasma chamberand the inductively coupled plasma source. In some embodiments, theultraviolet light source(s) can be located adjacent a window such thatone or more ultraviolet light beams from the ultraviolet light source(s)can pass through the window to reach an inner wall of the plasmachamber. For instance, the window can have at least one of: syntheticquartz, UV-grade sapphire, magnesium fluoride (MgF₂) material, orcalcium fluoride (CaF₂) material. A space between the ultraviolet lightsource(s) and the window can be filled with an inert gas to reduceabsorption by atmospheric oxygen. The inert gas can include at least oneof: helium, neon, argon and/or nitrogen.

In some embodiments, the ultraviolet light source(s) can be operated ina pulsed mode or turned on just before or during initiation of RF powerintroduction to an inductively coupled plasma source. Radiation from theultraviolet light source(s) can be maintained at least until the plasmaattains some minimal fraction of its ultimate density. In someembodiments, the radiation can be aimed at one or more interior wallareas that are proximate to an exterior inductively coupling element.

According to example aspects of the present disclosure, an inductiveplasma source of the type having superior suitability for ultra-cleansemiconductor processing can include low wall sputter and low plasmacontamination. The disclosed inductive plasma source can substantiallyimprove reliability and speed of plasma ignition while also havingsuperior cleanliness. For instance, a plasma processing apparatus caninclude a plasma chamber (e.g., an evacuated vessel), a dielectric wallforming at least a portion of the plasma chamber, and an inductivecoupling element (e.g., an inductive coupled plasma source, such as aninduction coil or an antenna) located proximate the dielectric wall. Theinductive coupling element can be connected to a supply of RF power. Theplasma processing apparatus can further include a controllable supply ofprocess gas to the plasma chamber interior, and a separatelycontrollable source of ultraviolet radiation (e.g., one or moreultraviolet light beams).

In some embodiments, a plasma processing apparatus can be configuredsuch that a substantial fraction of an ultraviolet radiation from anultraviolet source can have a line of sight through an at leastpartially ultraviolet-transparent window in a plasma chamber. Theultraviolet radiation can intercept at least a portion of an interiorsurface of the plasma chamber such that the ultraviolet radiation can beabsorbed on surfaces adjacent plasma when in operation (e.g., in aplasma region). In some embodiments, the ultraviolet light source canhave instantaneous power of several Watts or more of radiation emissionduring operation of which at least 1% and preferably 10% or more is in ahard-ultraviolet band, e.g., in a wavelength range of about 100nanometers to about 350 nanometers, such as a wavelength range of about180 nanometers to about 250 nanometers. The ultraviolet light source canbe a lamp that is separate and isolated from an inductive couplingelement. In some embodiments the ultraviolet light source can employ agas or gases that produce radiation in the hard-ultraviolet band(Wavelength less than about 250 nm). The ultraviolet light source can beturned on or the ultraviolet light source can start pulsing toilluminate a part of an interior surface of the plasma chamber, prior toor simultaneous with a turning-on of RF power to ignite a plasma in theplasma chamber. As such, reliability of ignition and growth of theplasma can be accelerated and improved.

In some embodiments, the inductive coupling element (e.g., an antennafor inductive coupling of RF power to plasma) can have reducedcapacitive coupling to dielectric walls of the plasma chamber, and toplasma during operation. In some embodiments, the inductive couplingelement can be separated by a substantial physical gap from a dielectricportion (e.g., a dielectric wall) of the plasma chamber such thatcapacitive coupling of the inductive coupling element to plasma can bereduced. In some embodiments, the inductive coupling element can belocated at a distance greater than a radius of the inductive coil. Insome embodiments, those part(s) of the inductive coupling element thatare physically closest to the dielectric portion of the plasma chambercan be grounded, or connected through a tunable reactance that can havelow impedance (e.g., less than about 5 Ohms) to electrical ground.

In some embodiments, the plasma processing apparatus can further includeone or more pieces of conducting material that can be interposedpartially or fully between the inductive coupling element and thedielectric portion of the plasma chamber. The one or more pieces ofconducting material can be connected electrically, either directly orthrough a tunable circuit, to ground thereby forming electrostaticshielding that mitigates capacitive coupling of the inductive couplingelement to the plasma. As such, plasma potential can be reduced andenergy of ions bombarding the plasma chamber wall can be reduced.

In some example conventional plasma processing apparatus, capacitivecoupling of an inductive coupling element to plasma can be sufficientlyweak so that normal plasma ignition can become unreliable or require toomuch time, e.g., during which electrical stresses are often large in RFpower components and electric fields large near the inductive couplingelement. This slow ignition can be generally the case because inductivedischarges generally start in the “E” mode where capacitive couplinginitiates the breakdown and then transitions to the “H” mode wherein theinductive coupling takes over sustaining the plasma as it provides themajority of power for electrons doing ionization. In conventionalinductive plasma processing apparatus, capacitive electric fields can belarger but more localized than the inductive electric fields.

According to example aspects of the present disclosure, the plasmaprocessing apparatus can have various features for mitigation ofcapacitive coupling from the inductive coupling element to the plasma,while successfully igniting plasmas rapidly and consistently withoutemploying much higher RF current and RF power levels to the inductivecoupling element than those employed for the conventional plasmaprocessing apparatus in steady state operation. In some embodiments,ultraviolet radiation from the ultraviolet light source can promoteplasma ignition and growth by ejecting photo-electrons from anirradiated surface(s) into dilute gas proximate what will be a plasmaregion (once ignited) as RF power is applied to the inductive couplingelement. These electrons can then be accelerated by electrical fields inthe plasma region to cause ionization of the gas in the plasma chamber.The ionization can then provide additional electrons that take part in“avalanche” of ionization which forms the plasma. In some embodiments, aplasma-facing surface irradiated with the ultraviolet radiation can be apart of a dielectric or metal wall of the plasma chamber. The dielectricor metal wall can have substantial induction electric fields when RFpower is being provided. In some embodiments, the ultraviolet irradiatedsurface can be a metal surface on an interior of the plasma chamber thathas a line of sight to the plasma region.

In some embodiments, metal surfaces that are not electrically floating(e.g., are electrically grounded) are desired since they do not chargeup so as to prevent electron emission as electrons are ejected from thesurface. Further, the energy required for electron photo-emission isless in conducting materials than in insulating materials sinceconduction band electrons require less energy to be ejected than valenceband electrons from solids. Further, metal walls do not charge-upresulting in trapping of emitted electrons as insulating materials cando.

In some embodiments, ultraviolet light sources for promotion of plasmaignition can have total instantaneous radiation output of about 1 Wattor more with output emission spectrum having at least 5% of power in thehard-ultraviolet band (e.g., in a wavelength range less than about 250nanometers). Examples of such ultraviolet light sources can includeXenon flashlamps, Deuterium lamps, excimer lamps or other any suitablelight sources that meet the above features. In some embodiments, awindow in the plasma chamber can be made of material transmissive ofhard-ultraviolet radiation. The window can have at least one ofsynthetic quartz, UV-grade Sapphire, or more highly UV transmissivematerials such as MgF₂ or CaF₂. In some embodiments, the window can be avacuum window with atmospheric pressure gas around the ultraviolet lightsource. For instance, a space between the ultraviolet light source andthe window can be filled with an inert gas (e.g., helium, argon, neon,and/or nitrogen) to reduce absorption by atmospheric oxygen.

In some embodiments, the hard-ultraviolet band of the ultraviolet lightsource can include a wavelength range that between about 115 nanometersand about 180 nm. This band can be referred to as “Vacuum Ultraviolet”(VUV), since these wavelengths are strongly absorbed by oxygen, such asin oxygen in air. In some embodiments, the ultraviolet radiation canhave 10% or more its electromagnetic radiation output in a VUV part of aspectrum of the ultraviolet light source. The instantaneous output powerin the hard-UV band at the time of plasma ignition can be about 0.1 Wattor more. This photon energy can be helpful because the photo-emission ofan electron from an insulator requires such photon energy that it canraise a valence electron past the conduction band and into the freeelectron energy space. For photoemission from metal, photon energy fromthe ultraviolet light source can raise an electron from a conductionband to a free state. In some embodiments, the photo-electron emissionfrom the interior surface of the plasma chamber can include at least 100electrons. To reduce heat buildup in an ultraviolet light source(s)(e.g., lamp), the ultraviolet light source can be pulsed with multiplevery short pulses at short intervals (e.g., less than about 100milliseconds and preferably less than 10 milliseconds). The ultravioletlight source can start pulsing prior to or just following the time ofinitiation of RF power supplied to the inductive coupling element. Insome embodiments, the ultraviolet radiation pulses can have a frequencyof at least about 100 per second so that a UV radiation pulse will occurwithin about 10 milliseconds after the electric field strength iscapable of initiating breakdown thereby reducing the total time at highlevel RF power for the ignition process.

In some embodiments, the ultraviolet light source can be a xenon arcflashlamp with an ultraviolet window or a VUV window that producesultraviolet light in the hard-ultraviolet band or in the VUV band. Insome embodiments, the xenon arc flashlamp can be small (e.g., less thanor about 1 inch for all dimensions). In some embodiments, the xenon arcflashlamp can be a high-pressure arc lamp that can pulse up to about 300Hertz (Hz) and operate at an average power level less than about 10Watts. In some embodiments, an arc lamp can produce strong continuumradiation down to about 100 nanometers in wavelength. In someembodiments such a small flashlamp might be positioned within the volumewhere the gas pressure is low and the plasma would otherwise occupy.Such a small flashlamp might be “plugged-in” within the plasma chamber,in some embodiments in a recessed volume embedded into a metal ordielectric structure. The arc lamp can have pulse energy about 100millijoules (mJ) to produce at least about 10¹⁵ hard-ultraviolet photonsper pulse with the photoelectron efficiency of at least about 1%producing orders of magnitude of more photoelectrons than needed.

In some embodiments, the ultraviolet light source can be a deuterium VUVlamp with MgF₂ window. The deuterium VUV lamp can be a high-pressuredeuterium arc lamp with radiation substantially in a band at about 160nanometers. The high-pressure deuterium arc lamp can be a continuouswave (CW) VUV source, not pulsed. In some embodiments, there is an about25 seconds warm-up time for these lamps, so it is important to turn thedeuterium VUV lamp on about 10 seconds to 30 seconds before ignition isdesired and off in synchrony with plasma reaching a full power.Provision should be made for cooling such a lamp since continuousoperation produces substantial heat. Life of such lamp can be at leastabout 1000 hours, which can be adequate for about 100,000 ignitions,which can be adequate for at least about 2 months of 24×7 processoperation.

In some embodiments, the ultraviolet light source can be an excimerRF/pulse xenon lamp. For instance, the excimer xenon lamp can be ahighly efficient source of about 172 nanometers radiation. The excimerxenon lamp can have long lifetime (e.g., longer than about 10,000hours).

In some embodiments, the ultraviolet light source(s) for acceleration ofplasma ignition can illuminate area(s) of the inner wall of the plasmachamber through a vacuum window of the plasma chamber. The vacuum windowcan be at least partially transparent to ultraviolet radiation. In someembodiments, the vacuum window can be highly transmissive of ultravioletlight such as MgF₂, CaF₂ or similar materials. In some embodiments, thevacuum window can have materials such as “synthetic quartz” materialsthat have better UV transmission than natural or conventional quartzdown to wavelengths of about 150 nm. Such window materials can have atleast 20% transmission of ultraviolet light in a wavelength range offrom about 115 nanometers to about 200 nanometers. In some embodiments,the ultraviolet light source can be mounted adjacent or near to thevacuum window in a vacuum wall (e.g., a dielectric part of the vacuumwall, and/or a metal part of the vacuum wall) of the plasma chamber. Insome embodiments, a space between the ultraviolet light source and thevacuum window can be purged or filled with helium or nitrogen to reduceUV loss due to absorption by atmospheric oxygen.

In some embodiments, ultraviolet radiation from the ultraviolet lightsource can be incident on a surface on the inside of the plasma chamber.The surface in some embodiments can be adjacent a volume withsubstantial induction electric field such that photoelectrons canprovide a substantial density in the plasma region where the gasbreakdown and plasma ignition avalanche occur. In some embodiments, athreshold for plasma ignition can be lowered to about the same powerdensity level as is used for sustaining the plasma, e.g., power densityas much as about 70% less than the RF power for a normal plasma ignitionthreshold.

In some embodiments, the plasma processing chamber can include a smalleradjacent chamber that is separated from a plasma chamber by anultraviolet transmissive window. For instance, such small adjacentchamber can be a sealed chamber having at least two electrodes and ahigh-pressure inert gas such as xenon. The window between the smalleradjacent chamber and the main plasma chamber can in part be made of aVUV transmissive material such as synthetic quartz. Ignition of plasmacan be then facilitated by supplying appropriate pulsed DC power to theelectrodes in the adjacent chamber such that plasma is rapidly struck inthe adjacent chamber and produces copious VUV radiation that illuminatesdielectric wall(s) and/or metal wall(s) of the plasma chamber throughthe window.

Example aspects of the present disclosure are directed to a plasmaprocessing apparatus. The plasma processing can include a plasmachamber, a dielectric wall forming at least a portion of the plasmachamber, an inductive coupling element located proximate the dielectricwall, an ultraviolet light source (e.g., CW lamp or pulsed lamp, suchas, a xenon arc flashlamp, deuterium lamp, or an excimer RF/pulse xenonlamp) to emit an ultraviolet light beam onto a metal surface or adielectric surface in the plasma chamber. The metal surface or adielectric surface can emit one or more electrons into the plasmachamber when the ultraviolet light beam is incident on the metal surfaceor a dielectric surface. The plasma processing apparatus can furtherinclude a controller to control the power to the ultraviolet lightsource and thereby the emission of ultraviolet light beam upon the metalsurface or the dielectric surface prior to or during ignition of aplasma in a process gas by energizing the inductive coupling elementwith a radio frequency (RF) energy (e.g., exciting with RF energy).

In some embodiments, the controller (e.g., a computer,microcontroller(s), other control device(s), etc.) can include one ormore processors and one or more memory devices. The one or more memorydevices can store computer-readable instructions that when executed bythe one or more processors cause the one or more processors to performoperations, such as turning on the ultraviolet light source to emit theultraviolet light beam on the metal surface or the dielectric surfaceprior to or during ignition of a plasma, or other suitable operation.

In some embodiments, the plasma chamber can further include one or morereflective elements (e.g., mirrors) reflect the light beam onto themetal surface or the dielectric surface. In some embodiments, the metalsurface and/or dielectric surface can be electrically grounded. In someembodiments, the ultraviolet light source can emit the light beam in awavelength range from about 100 nanometers to about 250 nanometers. Insome embodiments, the plasma processing apparatus can include anelectrostatic shield (e.g., a Faraday shield, or other suitableconductive materials) located between the dielectric wall and theinductive coupling element. In some embodiments, the ultraviolet lightbeam can pass through a vacuum window to reach the metal surface and/ordielectric surface. The vacuum window (e.g., synthetic quartz, UV-gradesapphire, magnesium fluoride (MgF2) material, or calcium fluoride (CaF2)material) can be at least partially transparent to the ultraviolet lightbeam. In some embodiments, a space between the ultraviolet light sourceand the window can be filled with a gas (e.g., helium or nitrogen) toreduce absorption by atmospheric oxygen. In some embodiments, the plasmachamber can be separated (e.g., by a separation grid) from a processingchamber having a workpiece support configured to support a workpiece.

Example aspects of the present disclosure are directed to a method forigniting a plasma in a plasma processing apparatus. The method caninclude admitting a process gas into a plasma chamber. The method caninclude exciting an inductive coupling element to initiate ignition ofthe plasma in the process gas. Prior to or during excitation of theinductive coupling element for the purpose of ignition of the plasma inthe process gas, the method can include emitting an ultraviolet light,via an ultraviolet light source, onto a metal surface and/or dielectricsurface in the plasma chamber. The metal surface and/or dielectricsurface can emit one or more electrons into the plasma chamber when theultraviolet light beam is incident on the metal surface or a dielectricsurface. The method can include energizing the inductive couplingelement with a radio frequency (RF) energy to sustain the plasma in theprocess gas.

Aspects of the present disclosure are discussed with reference to a“workpiece” that is a “semiconductor wafer” for purposes of illustrationand discussion. Those of ordinary skill in the art, using thedisclosures provided herein, will understand that the example aspects ofthe present disclosure can be used in association with any semiconductorsubstrate or other suitable substrate. In addition, the use of the term“about” in conjunction with a numerical value is intended to refer towithin ten percent (10%) of the stated numerical value.

Example aspects of the present disclosure can provide a number oftechnical effects and benefits. For instance, a plasma processingapparatus can include an ultraviolet light source can be controlled toemit the ultraviolet light beam on a metal surface or on a dielectricsurface prior to or during ignition of a plasma in a process gas byenergizing the inductive coupling element with a radio frequency (RF)energy. As such, the plasma processing apparatus can improve ignition ofplasma with a lower RF power level and can also improve speed andreliability of plasma ignition for semiconductor wafers. The plasmaprocessing apparatus can also reduce sputtering, particle contamination,and roughening of the inner walls of the plasma chamber.

FIG. 1 depicts an example plasma processing apparatus 100 according toexample embodiments of the present disclosure. As illustrated, theplasma processing apparatus 100 includes a processing chamber 110 and aplasma chamber 120 that is separated from the processing chamber 110.The processing chamber 110 includes a substrate holder or workpiecesupport 112 operable to hold a workpiece 114 to be processed, such as asemiconductor wafer. In this example illustration, a plasma is generatedin the plasma chamber 120 (i.e., plasma generation region 170) by aninductively coupled plasma source 135 and desired species are channeledfrom the plasma chamber 120 to the surface of substrate 114 through aseparation grid assembly 200.

Aspects of the present disclosure are discussed with reference to aninductively coupled plasma source for purposes of illustration anddiscussion. Those of ordinary skill in the art, using the disclosuresprovided herein, will understand that any plasma source (e.g.,inductively coupled plasma source, capacitively coupled plasma source,etc.) can be used without deviating from the scope of the presentdisclosure. In particular, in some embodiments there need not be aseparation, baffle or grid between plasma generation and substratesupport volumes.

The plasma chamber 120 includes a dielectric side wall 122 and a ceiling124. The dielectric side wall 122, the ceiling 124, and the separationgrid 200 define a plasma chamber interior 125. The dielectric side wall122 can be formed from a dielectric material, such as quartz and/oralumina. The inductively coupled plasma source 135 can include aninduction coil 130 disposed adjacent to the dielectric side wall 122above the plasma chamber 120. The induction coil 130 is coupled to an RFpower generator 134 through a suitable matching network 132. Processgases (e.g., reactant and/or carrier gases) can be provided to thechamber interior from a gas supply 150 and an annular gas distributionchannel 151 or other suitable gas introduction mechanism. When theinduction coil 130 is energized with RF power from the RF powergenerator 134, a plasma can be generated in the plasma chamber 120. In aparticular embodiment, the plasma processing apparatus 100 can includean optional grounded Faraday shield 128 to reduce capacitive coupling ofthe induction coil 130 to the plasma. In some embodiments the Faradayshield need not be directly grounded but may be grounded through atunable reactive circuit that may be tuned to a low reactive impedance.

As shown in FIG. 1, the separation grid 200 separates the plasma chamber120 from the processing chamber 110. The separation grid 200 can be usedto perform ion filtering from a mixture generated by plasma in theplasma chamber 120 to generate a filtered mixture. The filtered mixturecan be exposed to the workpiece 114 in the processing chamber 110.

According to example aspects of the present disclosure, ignition ofinductively coupled plasma can be improved with an ultraviolet lightsource that emits an ultraviolet light beam onto a dielectric walland/or a metal surface at a location proximate the volume that will beoccupied by plasma following ignition of the plasma. As such, less powercan be used to ignite the plasma with better igniting repeatability andto reduce a direct electric field ion bombardment to a dielectricwindow.

As can be seen in FIG. 1, the plasma processing chamber 100 furtherincludes an ultraviolet light source 160 and an ultraviolet (UV)emission assembly 162.

The ultraviolet light source 160 is mounted external to the plasmachamber 120 for the inductively coupled plasma source 135 such thatradiation from the ultraviolet light source 160 can illuminate an innerwall of the UV emission assembly 162 prior to or during ignition of theplasma. The ultraviolet light source 160 emits one or more ultravioletlight beams 164 (e.g., in a wavelength range of about 100 nanometers toabout 250 nanometers) into the plasma chamber 120 through the UVemission assembly 162. The ultraviolet light source 160 can be a CW lampor a pulsed lamp. Examples of the ultraviolet light source 160 caninclude a xenon arc flashlamp, deuterium lamp, an excimer RF/pulse xenonlamp, or any other suitable light source that emits an ultraviolet lightbeam. For instance, the ultraviolet light source 160 can be turned on orthe ultraviolet light source 160 can start pulsing to illuminate a partof an interior surface of the UV emission assembly 162, prior to orsimultaneous with a turning-on of RF power 134 to ignite the plasma inthe plasma chamber 120. Radiation from the ultraviolet light source 160can be maintained at least until the plasma attains a substantialfraction of its ultimate density. As such, reliability of ignition andgrowth of the plasma can be accelerated and improved.

In some embodiments, to reduce heat buildup in the ultraviolet lightsource 160, the ultraviolet light source 160 can be pulsed with multiplerapid pulses (e.g., less than about 1 millisecond) at very shortintervals (e.g., less than about 10 milliseconds). The ultraviolet lightsource 160 can start pulsing prior to or just following the time ofinitiation of RF power 134 supplied to the inductively coupled source135. In some embodiments, the ultraviolet radiation pulses can have afrequency of at least about 10 per second and preferably 100 per secondor more so that multiple pulses can contribute ultraviolet photons to anignition process. As such, ultraviolet acceleration of plasma ignitioncan only take about 10 milliseconds.

In some embodiments, ultraviolet radiation from the ultraviolet lightsource 160 can promote plasma ignition and growth by ejectingphoto-electrons from an irradiated surface(s) proximate the plasmaregion 170 as the RF power 134 is applied to the inductively coupledplasma source 135, as further described below. The irradiated surfacemay be metal or insulator material or metal with a very thin insulatorsurface layer.

In some embodiments (not shown in FIG. 1), the plasma processingapparatus 100 can include a controller that controls the ultravioletlight source 160 to emit the ultraviolet light beam. The controller(e.g., a computer, microcontroller(s), other control device(s), etc.)can include one or more processors and one or more memory devices. Theone or more memory devices can store computer-readable instructions thatwhen executed by the one or more processors cause the one or moreprocessors to perform operations, such as turning on the ultravioletlight source to emit the ultraviolet light beam on a metal surface or adielectric surface prior to or during ignition of a plasma, or othersuitable operation.

The UV emission assembly 162 includes one or more walls 166, one or morereflective elements (e.g., mirrors) 168 and a vacuum window 172. Thestructure 162 may be electrically grounded so that the surfaces 166 and174 are grounded. At least a portion of the wall(s) 166 can be metal,and/or dielectric. When the ultraviolet light beam 164 is incident on asurface 174 (e.g., a metal surface or a dielectric surface) at alocation proximate the plasma, the surface 174 can emit one or moreelectrons into the plasma region 170. In some embodiments, aninstantaneous output power of the ultraviolet light source 160 at thetime of plasma ignition can be about 1 Watt or more. This can be becausethe photo-emission of an electron from an insulator requires such photonenergy that it can raise a valence electron past the conduction band andinto the free electron energy space. For photoemission from metal,photon energy from the ultraviolet light source 160 can raise anelectron from a conduction band to a free state which typically takesless photon energy. In some embodiments, the photo-electron emissionfrom the surface 174 of the UV emission assembly 162 can include atleast 1000 electrons in a pulse.

In some embodiments, electrons emitted from the surface 174 into thevolume 125 can then be accelerated by electrical fields in the volume125 to cause ionization of the gas in the plasma chamber 120. Typically,as the plasma develops and shields the plasma nearer the chamber axis ofthe dielectric vessel 122 the induction fields are much stronger nearthe inner surface of the dielectric vessel 122. The ionization can thenprovide additional electrons that take part in “avalanche” of ionizationwhich forms the plasma. In some embodiments (not shown in FIG. 1), aplasma-facing surface irradiated with ultraviolet radiation can be apart of a dielectric wall of a plasma chamber, as further described inFIG. 3. The dielectric wall can have substantial induction electricfields when an RF power is being provided. In some embodiments (notshown in FIG. 1), ultraviolet irradiated surface can be a metal surfaceon an interior of a plasma chamber that has a line of sight to thevolume within the vessel 122 that is close to the coil 130, as furtherdescribed in FIG. 4.

As can be seen in FIG. 1, the ultraviolet light beam 164 is reflectedonto the surface 174 via a reflective element (e.g., a mirror) 168.Electrons 176 emitted from the surface 174 pass into the plasma region170.

The vacuum window 172 separates the UV source 160 from the reflector168, the surface 174 and surface 166 that are exposed to the plasmachamber interior 125 . The vacuum window 172 can be an ultraviolettransmissive window. For instance, the window 172 can have at least oneof: synthetic quartz, UV-grade sapphire, magnesium fluoride (MgF₂)material, or calcium fluoride (CaF₂) material. As another example, aspace between the ultraviolet light source(s) and the window can befilled with a gas (e.g., helium or nitrogen) to reduce absorption byatmospheric oxygen.

In some embodiments (not shown in FIG. 1), the UV emission assembly canbe a sealed chamber having at least two electrodes and a high-pressureinert gas such as xenon. The vacuum window can in part be made of a VUVtransmissive material such as synthetic quartz. Ignition of plasma canbe then facilitated by supplying appropriate pulsed electric power tothe electrodes in the UV emission assembly such that that the UVemission assembly experiences electric breakdown and to produce copiousVUV radiation that illuminates dielectric wall(s) and/or metal wall(s)of the plasma chamber.

FIG. 2 depicts a flow diagram of an example method (230) foraccelerating ignition of an inductively coupled plasma according toexample aspects of the present disclosure. The method (230) can beimplemented using the plasma processing apparatus 100. However, as willbe discussed in detail below, the methods according to example aspectsof the present disclosure can be implemented using other approacheswithout deviating from the scope of the present disclosure. FIG. 2depicts steps performed in a particular order for purposes ofillustration and discussion. Those of ordinary skill in the art, usingthe disclosures provided herein, will understand that various steps ofany of the methods described herein can be omitted, expanded, performedsimultaneously, rearranged, and/or modified in various ways withoutdeviating from the scope of the present disclosure. In addition, variousadditional steps (not illustrated) can be performed without deviatingfrom the scope of the present disclosure.

At (240), the method can include placing a workpiece on a workpiecesupport. For instance, a workpiece 114 can be placed on a workpiecesupport 112 in a processing chamber 110.

At (250), the method can include admitting a process gas into a plasmachamber. For instance, a process gas can be admitted into the plasmachamber interior 125 from the gas source 150 via the annular gasdistribution channel 151 or other suitable gas introduction mechanism.

At (260), prior to or during initiation of providing RF power to theinduction coil, the method can include emitting an ultraviolet lightbeam, via an ultraviolet light source, onto a metal surface and/ordielectric surface in the plasma chamber. The metal surface and/ordielectric surface can emit one or more electrons into the plasmachamber when the ultraviolet light beam is incident on the metal surfaceand/or dielectric surface. For instance, prior to or during ignition ofthe plasma in the process gas, an ultraviolet light source 160 can emitan ultraviolet light beam 164 that passes through a transmissive vacuumwindow and is reflected onto a surface 174 via a reflective element(e.g., a mirror) 168. Electrons 176 emitted from the surface 174 passdirectly into the plasma region 170 because the surface 174 has directline of sight to the plasma region 170 and plasma chamber interior 125.

At (270), the method can include energizing or continuing to energizethe inductive coupling element with a radio frequency (RF) energy tosustain the plasma in the process gas. For instance, the induction coil130 can be energized with the RF power generator 134 to sustain theplasma in the process gas.

At (280), the method can include exposing the workpiece to one or morespecies generated by the plasma. For instance, one or species generatedby the plasma can be channeled from the plasma chamber 120 to surface ofthe workpiece114 through the separation grid assembly 200.

FIG. 3 depicts an example plasma processing apparatus 300 according toexample embodiments of the present disclosure. The plasma processingapparatus 300 is similar to the plasma processing apparatus 100 of FIG.1.

More particularly, plasma processing apparatus 300 includes a processingchamber 110 and a plasma chamber 120 that is separated from theprocessing chamber 110. Processing chamber 110 includes a substrateholder or workpiece support 112 operable to hold a workpiece 114 to beprocessed, such as a semiconductor wafer. In this example illustration,a plasma is generated in plasma chamber 120 (i.e., plasma generationregion 330) by an inductively coupled plasma source 135 and desiredspecies are channeled from the plasma chamber 120 to the surface ofsubstrate 114 through a separation grid assembly 200. In someembodiments, there is no separation grid or other structure between theplasma chamber 120 and the processing chamber 110.

The plasma chamber 120 includes a dielectric side wall 122 and a ceiling124. The dielectric side wall 122, ceiling 124, and separation grid 200define a plasma chamber interior 125. Dielectric side wall 122 can beformed from a dielectric material, such as quartz and/or alumina. Theinductively coupled plasma source 135 can include an induction coil 130disposed adjacent to the dielectric side wall 122 above the processingchamber 120. The induction coil 130 is coupled to an RF power generator134 through a suitable matching network 132. Process gases (e.g., aninert gas) can be provided to the chamber interior from gas supply 150or other suitable gas introduction mechanism. When the induction coil130 is energized with RF power from the RF power generator 134, a plasmacan be generated in the plasma chamber 120. In a particular embodiment,the plasma processing apparatus 500 can include an optional groundedFaraday shield 128 to reduce capacitive coupling of the induction coil130 to the plasma.

According to example aspects of the present disclosure, ultravioletlight source(s) can be located adjacent a window such that one or moreultraviolet light beams from the ultraviolet light source(s) can passthrough the window to reach an inner wall of a plasma chamber. Forinstance, as can be seen in FIG. 3, the plasma processing chamber 300further includes an ultraviolet light source 160 and a vacuum window310.

The ultraviolet light source 160 is mounted adjacent the vacuum window310 such that an ultraviolet light beam 320 from the ultraviolet lightsource 160 passes through the window 310 to reach an interior surface340 of the dielectric wall 122 of the plasma chamber 120. The interiorsurface 340 is proximate a plasma region 330 (or a plasma in the plasmaregion 330). As can be seen in FIG. 3, the ultraviolet light beam 320intercepts a portion of the interior surface 340 of the plasma chamber120 such that the ultraviolet light beam 320 is incident upon theinterior surface 340 at a location adjacent plasma in operation.

The ultraviolet light source 160 can be a CW lamp or a pulsed lamp.Examples of the ultraviolet light source 160 can include a xenon arcflashlamp, deuterium lamp, an excimer RF/pulse xenon lamp, or any othersuitable light source that emits an ultraviolet light beam. Forinstance, the ultraviolet light source 160 can be turned on or theultraviolet light source 160 can start pulsing to illuminate a part ofthe interior surface 340 of the dielectric wall 122, prior to orsimultaneous with a turning-on of RF power 134 to ignite the plasma inthe plasma chamber120. Radiation from the ultraviolet light source 160can be maintained at least until the plasma attains a fraction of itsultimate density. As such, reliability of ignition and growth of theplasma can be accelerated and improved.

In some embodiments, to reduce heat buildup in the ultraviolet lightsource 160, the ultraviolet light source 160 can be pulsed with multiplerapid pulses at very short intervals (e.g., less than 10 milliseconds).The ultraviolet light source 160 can start pulsing prior to or justfollowing the time of initiation of RF power 134 supplied to theinductively coupled source 135. In some embodiments, the ultravioletradiation pulses can have a frequency of at least about 100 and in someembodiments 500 per second so that multiple pulses can contributeultraviolet photons to an ignition process. As such, ultravioletacceleration can only take about 10 milliseconds.

In some embodiments, ultraviolet radiation from the ultraviolet lightsource 160 can promote plasma ignition and growth by ejecting electronsfrom an irradiated surface(s) proximate the plasma as the RF power 134is applied to the inductively coupled plasma source 135. When theultraviolet light beam 320 is incident on the interior surface 340(e.g., a dielectric surface) at a location proximate the plasma, thesurface 340 can emit one or more electrons into the plasma region 330.In some embodiments, an instantaneous output power of the ultravioletlight source 160 at the time of plasma ignition can be about 1 Watt ormore. This can be because the photo-emission of an electron from aninsulator requires such photon energy that it can raise a valenceelectron past the conduction band and into the free electron energyspace. In some embodiments, the photo-electron emission from the surface340 can include at least 5000 electrons. In some embodiments, electronsemitted from the surface 340 can then be accelerated by electricalfields in the plasma region 330 to cause ionization of the gas in theplasma chamber 120. The ionization can then provide additional electronsthat take part in “avalanche” of ionization which forms the plasma. Insome embodiments there may be a thin metal coating on the dielectricwall that may intercept the UV radiation from the source 160.

In some embodiments (not shown in FIG. 3), the plasma processingapparatus 300 can include a controller that controls the ultravioletlight source 160 to emit the ultraviolet light beam 320. The controller(e.g., a computer, microcontroller(s), other control device(s), etc.)can include one or more processors and one or more memory devices. Theone or more memory devices can store computer-readable instructions thatwhen executed by the one or more processors cause the one or moreprocessors to perform operations, such as turning on the ultravioletlight source to emit the ultraviolet light beam on a dielectric surfaceprior to or during ignition of a plasma, or other suitable operation.

The vacuum window 310 can be one example embodiment of the vacuum window172. For instance, the window 310 can have at least one of: syntheticquartz, UV-grade sapphire, magnesium fluoride (MgF2) material, orcalcium fluoride (CaF2) material. As another example, a space betweenthe ultraviolet light source 160 and the window 310 can be filled with agas (e.g., helium, nitrogen, argon, and/or nitrogen) to reduceabsorption by atmospheric oxygen.

FIG. 4 depicts an example plasma processing apparatus 400 according toexample embodiments of the present disclosure. The plasma processingapparatus 400 is similar to the plasma processing apparatus 100 of FIG.1 and the plasma processing apparatus 300 of FIG. 3.

More particularly, plasma processing apparatus 400 includes a processingchamber 110 and a plasma chamber 120 that is separated from theprocessing chamber 110. Processing chamber 110 includes a substrateholder or workpiece support 112 operable to hold a workpiece 114 to beprocessed, such as a semiconductor wafer. In this example illustration,a plasma is generated in plasma chamber 120 (i.e., plasma generationregion 420) by an inductively coupled plasma source 135 and desiredspecies are channeled from the plasma chamber 120 to the surface ofsubstrate 114 through a separation grid assembly 200.

The plasma chamber 120 includes a dielectric side wall 122 and a ceiling124. The dielectric side wall 122, ceiling 124, and separation grid 200define a plasma chamber interior 125. Dielectric side wall 122 can beformed from a dielectric material, such as quartz, glass, alumina,silicon nitride, silicon oxynitride, aluminum nitride, aluminumoxynitride, or other high-temperature capable dielectric or combinationthereof. The inductively coupled plasma source 135 can include aninduction coil 130 disposed adjacent to the dielectric side wall 122above the plasma chamber 120. The induction coil 130 is coupled to an RFpower generator 134 through a suitable matching network 132. Processgases (e.g., an inert gas) can be provided to the chamber interior fromgas supply 150 or other suitable gas introduction mechanism. When theinduction coil 130 is energized with RF power from the RF powergenerator 134, a plasma can be generated in the plasma chamber 120. In aparticular embodiment, the plasma processing apparatus 500 can includean optional grounded Faraday shield 128 to reduce capacitive coupling ofthe induction coil 130 to the plasma.

As shown in FIG. 4, a separation grid 200 separates the plasma chamber120 from the processing chamber 110. The separation grid 200 can be usedto perform ion filtering from a mixture generated by plasma in theplasma chamber 120 to generate a filtered mixture. The filtered mixturecan be exposed to the workpiece 114 in the processing chamber.

According to example aspects of the present disclosure, ultravioletlight source(s) can be located adjacent a window such that one or moreultraviolet light beams from the ultraviolet light source(s) can passthrough the window to impinge on a metal surface 430 that may be of ametal structure 410 of a plasma chamber (e.g., a top cap). As can beseen in FIG. 4, the plasma processing chamber 400 further includes anultraviolet light source 160, a vacuum window 310 and a metal wall 410.The ultraviolet light source 160 is mounted adjacent the vacuum window310 such that an ultraviolet light beam 320 from the ultraviolet lightsource 160 passes through the window 310 to reach an interior surface430 of the metal wall 410 of the plasma chamber 120. The interiorsurface 430 is proximate a plasma region 420 (or a plasma in the plasmaregion 420). As can be seen in FIG. 4, the ultraviolet light beam 320intercepts a portion of the interior surface 410 of the plasma chamber120 such that the ultraviolet light beam 320 can pass through some partof the volume that may be occupied by plasma in operation and can alsopass through some part of the evacuated volume that may not be occupiedby plasma in operation.

The ultraviolet light source 160 can be a CW lamp or a pulsed lamp.Examples of the ultraviolet light source 160 can include a xenon arcflashlamp, deuterium lamp, an excimer RF /pulse xenon lamp, or any othersuitable light source that emits an ultraviolet light beam. Forinstance, the ultraviolet light source 160 can be turned on or theultraviolet light source 160 can start pulsing to illuminate a part ofthe interior surface 430 of the metal wall 410, prior to or simultaneouswith a turning-on of RF power 134 to ignite the plasma in the plasmachamber120. Radiation from the ultraviolet light source 160 can bemaintained at least until the plasma attains a fraction of its ultimatedensity. As such, reliability of ignition and growth of the plasma canbe accelerated and improved.

In some embodiments, to reduce heat buildup in the ultraviolet lightsource 160, the ultraviolet light source 160 can be pulsed with multiplerapid pulses at very short intervals (e.g., less than 50 millisecondsand more preferably less than 10 milliseconds). The ultraviolet lightsource 160 can start pulsing prior to or just following the time ofinitiation of RF power 134 supplied to the inductively coupled source135. In some embodiments, the ultraviolet radiation pulses can have afrequency of at least about 500 per second so that multiple pulses cancontribute ultraviolet photons to an ignition process. As such, thetotal duration of ultraviolet acceleration of plasma ignition can onlytake about 50 milliseconds and preferably less than 10 milliseconds.

In some embodiments, ultraviolet radiation from the ultraviolet lightsource 160 can promote plasma ignition and growth by ejecting electronsfrom an irradiated surface(s) proximate the volume that will be occupiedby plasma as the RF power 134 is applied to the inductively coupledplasma source 135. When the ultraviolet light beam 320 is incident onthe interior surface 430 (e.g., a metal surface) at a location proximatewhere the plasma will be, the surface 430 can emit one or more electronsinto the region 420 that the plasma will occupy. In some embodiments, aninstantaneous output power of the ultraviolet light source 160 at thetime of plasma ignition can be about 1 Watt or more, preferably afraction larger than 10% of which is in the hard UV band. This can bebecause the photo-emission of an electron from an insulator requiressuch photon energy that it can raise a valence electron past theconduction band and into the free electron energy space. In someembodiments, in one pulse of UV the photo-electron emission from thesurface 430 can include at least 1000 electrons.

In some embodiments, electrons emitted from the surface 430 can then beaccelerated by electrical fields in the region 420 induced by the rfcurrent in the induction coil to cause ionization of the gas in theplasma chamber 120 to fill the region 420 with plasma. The ionization ofgas in this region can then provide additional electrons that take partin “avalanche” of ionization which forms the plasma.

In some embodiments (not shown in FIG. 4), the plasma processingapparatus 400 can include a controller that controls the ultravioletlight source 160 to emit the ultraviolet light beam 320. The controller(e.g., a computer, microcontroller(s), other control device(s), etc.)can include one or more processors and one or more memory devices. Theone or more memory devices can store computer-readable instructions thatwhen executed by the one or more processors cause the one or moreprocessors to perform operations, such as turning on the ultravioletlight source to emit the ultraviolet light beam on a metal surface priorto or during ignition of a plasma, or other suitable operation.

The vacuum window 310 can be one embodiment of the vacuum window 172.For instance, the window 310 can have at least one of: synthetic quartz,UV-grade sapphire, magnesium fluoride (MgF2) material, or calciumfluoride (CaF2) material. As another example, a space between theultraviolet light source 160 and the window 310 can be filled with a gas(e.g., helium or nitrogen) to reduce absorption by atmospheric oxygen.

FIG. 5 depicts an example plasma processing apparatus 500 according toexample embodiments of the present disclosure. The plasma processingapparatus 500 is similar to the plasma processing apparatus 100 of FIG.1.

More particularly, plasma processing apparatus 500 includes a processingchamber 110 and a plasma chamber 120 that is separated from theprocessing chamber 110. Processing chamber 110 includes a substrateholder or workpiece support 112 operable to hold a workpiece 114 to beprocessed, such as a semiconductor wafer. In this example illustration,a plasma is generated in plasma chamber 120 (i.e., plasma generationregion) by an inductively coupled plasma source 135 and desired speciesare channeled from the plasma chamber 120 to the surface of substrate114 through a separation grid assembly 200.

The plasma chamber 120 includes a dielectric side wall 122 and a ceiling124. The dielectric side wall 122, ceiling 124, and separation grid 200define a plasma chamber interior 125. Dielectric side wall 122 can beformed from a dielectric material, such as quartz and/or alumina orother high temperature resistant dielectrics such as ceramics. Theinductively coupled plasma source 135 can include an induction coil 130disposed adjacent to the dielectric side wall 122 above the plasmachamber 120. The induction coil 130 is coupled to an RF power generator134 through a suitable matching network 132. Process gases can beprovided to the chamber interior from gas supply 150 and annular gasdistribution channel 151 or other suitable gas introduction mechanism.When the induction coil 130 is energized with RF power from the RF powergenerator 134, a plasma can be generated in the plasma chamber 120. In aparticular embodiment, the plasma processing apparatus 500 can includean optional grounded Faraday shield 128 to reduce capacitive coupling ofthe induction coil 130 to the plasma.

As shown in FIG. 5, a separation grid 200 separates the plasma chamber120 from the processing chamber 110. The separation grid 200 can be usedto perform ion filtering from a mixture generated by plasma in theplasma chamber 120 to generate a filtered mixture. The filtered mixturecan be exposed to the workpiece 114 in the processing chamber.

The example plasma processing apparatus 500 of FIG. 5 is operable togenerate a first plasma 502 (e.g., a remote plasma) in the plasmachamber 120 and a second plasma 504 (e.g., a direct plasma) in theprocessing chamber 110. As used herein, a “remote plasma” refers to aplasma generated remotely from a workpiece, such as in a plasma chamberseparated from a workpiece by a separation grid. As used herein, a“direct plasma” refers to a plasma that is directly exposed to aworkpiece, such as a plasma generated in a processing chamber having aworkpiece support operable to support the workpiece.

More particularly, the plasma processing apparatus 500 of FIG. 5includes a bias source having bias electrode 510 in the workpiecesupport 112. The bias electrode 510 can be coupled to an RF powergenerator 514 via a suitable matching network 512. When the biaselectrode 510 is energized with RF energy, a second plasma 504 can begenerated from a mixture in the processing chamber 110 for directexposure to the workpiece 114. The processing chamber 110 can include agas exhaust port 516 for evacuating a gas from the processing chamber110.

According to example aspects of the present disclosure, ignition ofinductively coupled plasma can be improved with an ultraviolet lightsource that emits an ultraviolet light beam onto a dielectric walland/or a metal surface at a location proximate to where the plasma willbe, prior to or during ignition of the plasma. As such, less power canbe used to ignite either or both of the plasmas with better ignitingrepeatability and to reduce a direct electric field ion bombardment to adielectric window.

As can be seen in FIG. 5, the plasma processing chamber 500 furtherincludes an ultraviolet light source 160 and a metal top structure 162containing a UV transmissive window 172. The ultraviolet light source160 is mounted external to the plasma chamber 120 for the inductivelycoupled plasma source 135 such that radiation from the ultraviolet lightsource 160 can illuminate an inner wall of the metal top structure 162prior to or during ignition of the plasma. The ultraviolet light source160 emits one or more ultraviolet light beams 164 into the plasmachamber 120 through the UV transmissive window 172. The ultravioletlight source 160 can be a CW lamp or a pulsed lamp. Examples of theultraviolet light source 160 can include a xenon arc flashlamp,deuterium lamp, an excimer RF/pulse xenon lamp, or any other suitablelight source that emits an ultraviolet light beam. For instance, theultraviolet light source 160 can be turned on or the ultraviolet lightsource 160 can start pulsing UV energy that is then transmitted throughwindow 172 to illuminate a part of an interior surface of the metal topstructure 162, that faces the interior of the plasma chamber, prior toor simultaneous with a turning-on of RF power 134 to ignite the plasmain the plasma chamber 120. Radiation from the ultraviolet light source160 can be maintained at least until the plasma attains a fraction ofits ultimate density or the voltage on the inductive coupling antennaexhibits a substantial and rapid change as the plasma occupies a portionof the interior of the chamber. As such, reliability of ignition andgrowth of the plasma can be accelerated and improved.

In some embodiments, to reduce heat buildup in the ultraviolet lightsource 160, the ultraviolet light source 160 can be pulsed with multiplerapid pulses at very short intervals (e.g., less than 10 milliseconds).The ultraviolet light source 160 can start pulsing prior to or justfollowing initiation of RF power 134 supplied to the inductively coupledsource 135. In some embodiments, the ultraviolet radiation pulses canhave a frequency of at least about 100 per second so that multiplepulses can contribute ultraviolet photons to an ignition process. Assuch, ultraviolet-assisted ignition of the plasma can only take about 50milliseconds or less.

In some embodiments, ultraviolet radiation from the ultraviolet lightsource 160 can promote plasma ignition and growth by ejectingphoto-electrons from an irradiated surface(s) proximate the region 502that will contain plasma as the RF power 134 is applied to theinductively coupled plasma source 135, as further described below.

In some embodiments (not shown in FIG. 5), the plasma processingapparatus 500 can include a controller that controls the ultravioletlight source 160 to emit the ultraviolet light beam. The controller(e.g., a computer, microcontroller(s), other control device(s), etc.)can include one or more processors and one or more memory devices. Theone or more memory devices can store computer-readable instructions thatwhen executed by the one or more processors cause the one or moreprocessors to perform operations, such as turning on the ultravioletlight source to emit the ultraviolet light beam on a metal surface or adielectric surface prior to or during ignition of a plasma, or othersuitable operation.

The metal top structure 162 includes one or more walls 166, one or morereflective elements (e.g., mirrors) 168 and a vacuum window 172. Thestructure 162 is electrically grounded or may be biased negatively withrespect to earth ground, particularly during the plasma ignition phase.At least a portion of the wall(s) 166 can be metal, and/or dielectric.When the ultraviolet light beam 164 is incident on a surface 174 (e.g.,a metal surface or a dielectric surface) at a location proximate thevolume that will contain the plasma, the surface 174 can emit one ormore electrons into the region 502. In some embodiments, aninstantaneous output power of the ultraviolet (UV) light source 160 atthe time of plasma ignition can be about 1 Watt or more. The wavelengthof at least part of the radiation may be less than about 250 nm, beingin the hard UV band. This can be because the photo-emission of anelectron from an insulator requires such photon energy that it can raisea valence electron past the conduction band and into the free electronenergy space. For photoemission from metal, photon energy from theultraviolet light source 160 can raise an electron from a conductionband to a free state. In some embodiments, the photo-electron emissionfrom the surface 174 of the UV emission assembly 162 can include atleast 100 electrons.

In some embodiments, electrons emitted from the surface 174 can then beaccelerated by electrical fields in the plasma region 502 to causeionization of the gas in the plasma chamber 120. The ionization can thenprovide additional electrons that take part in exponential growth“avalanche” of ionization which forms the plasma. In some embodiments(not shown in FIG. 5), an interior volume-facing surface irradiated withultraviolet radiation can be a part of a dielectric wall of a plasmachamber, as described above in FIG. 3. The dielectric wall can havesubstantial induction electric fields when an RF power is beingprovided. In some embodiments (not shown in FIG. 5), ultravioletirradiated surface can be a metal surface on an interior wall of aplasma chamber that has a line of sight to a region that will containplasma after ignition, as described above in FIG. 4.

As can be seen in FIG. 5, the ultraviolet light beam 164 is reflectedonto the surface 174 via a reflective element (e.g., a mirror) 168.Electrons 176 emitted from the surface 174 are emitted directly into theregion 502 that will contain plasma after ignition.

The vacuum window 172 separates the lamp 160 from the plasma chamberinterior 125. The vacuum window 172 can be an ultraviolet transmissivewindow. For instance, the window 172 can have at least one of: syntheticquartz, UV-grade sapphire, magnesium fluoride (MgF2) material, orcalcium fluoride (CaF2) material. As another example, a space betweenthe ultraviolet light source(s) and the window can be filled with a gas(e.g., helium or nitrogen) to reduce absorption by atmospheric oxygen.

In some embodiments (not shown in FIG. 5), the UV emission assembly canbe a sealed chamber having at least two electrodes and a high-pressureinert gas such as xenon. The vacuum window can in part be made of a UVtransmissive material such as synthetic quartz. Ignition of plasma canbe then facilitated by supplying appropriate RF power to the inductivecoupling element while there is fast pulsed DC power to the electrodesin the UV emission assembly such that that the UV emission assembly canproduce copious UV radiation that illuminates dielectric wall(s) and/ormetal wall(s) of the plasma chamber.

FIG. 6 depicts a plasma processing apparatus 600 similar to that of FIG.1 and FIG. 5. More particularly, plasma processing apparatus 600includes a processing chamber 110 and a plasma chamber 120 that isseparated from the processing chamber 110. Processing chamber 110includes a substrate holder or workpiece support 112 operable to hold aworkpiece 114 to be processed, such as a semiconductor wafer. In thisexample illustration, a plasma is generated in plasma chamber 120 (i.e.,plasma generation region) by an inductively coupled plasma source 135and desired gas phase species are channeled from the plasma chamber 120to the surface of substrate 114 through a separation grid assembly 200.

The plasma chamber 120 includes a dielectric side wall 122 and a ceiling124. The dielectric side wall 122, ceiling 124, and separation grid 200define a plasma chamber interior 125. Dielectric side wall 122 can beformed from a dielectric material, such as quartz and/or alumina. Theinductively coupled plasma source 135 can include an induction coil 130disposed adjacent the dielectric side wall 122 about the plasma chamber120. The induction coil 130 is coupled to an RF power generator 134through a suitable matching network 132. Process gas (e.g., an inertgas) can be provided to the chamber interior from gas supply 150 andannular gas distribution channel 151 or other suitable gas introductionmechanism. When the induction coil 130 is energized with RF power fromthe RF power generator 134, a plasma can be generated in the plasmachamber 120. In a particular embodiment, the plasma processing apparatus600 can include an optional grounded Faraday shield 128 to reducecapacitive coupling of the induction coil 130 to the plasma.

As shown in FIG. 6, a separation grid 200 separates the plasma chamber120 from the processing chamber 110. The separation grid 200 can be usedto perform ion filtering from a mixture generated by plasma in theplasma chamber 120 to generate a filtered mixture. The filtered mixturecan be exposed to the workpiece 114 in the processing chamber.

The example plasma processing apparatus 600 of FIG. 6 is operable togenerate a first plasma 602 (e.g., a remote plasma) in the plasmachamber 120 and a second plasma 604 (e.g., a direct plasma) in theprocessing chamber 110. As shown, the plasma processing apparatus 600can include an angled dielectric sidewall 622 that extends from thevertical sidewall 122 associated with the remote plasma chamber 120. Theangled dielectric sidewall 622 can form a part of the processing chamber110.

A second inductive plasma source 635 can be located proximate thedielectric sidewall 622. The second inductive plasma source 635 caninclude an induction coil 810 coupled to an RF generator 614 via asuitable matching network 612. The induction coil 610, when energizedwith RF energy, can induce a direct plasma 604 from a mixture in theprocessing chamber 110. A Faraday shield 628 can be disposed between theinduction coil 610 and the sidewall 622.

The workpiece support 112 can be movable in a vertical direction notedas “V.” For instance, the workpiece support 112 can include a verticallift 816 that can be configured to adjust a distance between theworkpiece support 112 and the separation grid assembly 200. As oneexample, the workpiece support 112 can be located in a first verticalposition for processing using the remote plasma 602. The workpiecesupport 112 can be in a second vertical position for processing usingthe direct plasma 604. The first vertical position can be closer to theseparation grid assembly 200 relative to the second vertical position.

The plasma processing apparatus 600 of FIG. 6 includes a bias sourcehaving bias electrode 510 in the workpiece support 112. The biaselectrode 510 can be coupled to an RF power generator 514 via a suitablematching network 512. The processing chamber 110 can include a gasexhaust port 516 for evacuating a gas from the processing chamber 110.

According to example aspects of the present disclosure, ignition ofinductively coupled plasma can be improved with an ultraviolet lightsource that emits an ultraviolet light beam onto a dielectric walland/or a metal surface at a location proximate the region wherein therewill be plasma once there is ignition of the plasma. As such, less powercan be used to ignite the plasma with better igniting repeatability andto reduce a direct electric field ion bombardment to a dielectricwindow.

As can be seen in FIG. 6, the plasma processing chamber 600 furtherincludes an ultraviolet light source 160 and a UV emission assembly 162.The ultraviolet light source 160 is mounted external to the plasmachamber 120 for the inductively coupled plasma source 135 such thatradiation from the ultraviolet light source 160 can illuminate an innerwall of the metal top structure 162 prior to or during ignition of theplasma. The ultraviolet light source 160 emits one or more ultravioletlight beams 164 (e.g., in a wavelength range of about 600 nanometers toabout 250 nanometers) into the plasma chamber 120 through the UVtransmissive window 172. The ultraviolet light source 160 can be a CWlamp or a pulsed lamp. Examples of the ultraviolet light source 160 caninclude a xenon arc flashlamp, deuterium lamp, an excimer RF/pulse xenonlamp, or any other suitable light source that emits an ultraviolet lightbeam. For instance, the ultraviolet light source 160 can be turned on orthe ultraviolet light source 160 can start pulsing to illuminate a partof an interior surface of the UV emission assembly 162, prior to orsimultaneous with a turning-on of RF power 134 to ignite the plasma inthe plasma chamber120. Radiation from the ultraviolet light source 160can be maintained at least until the plasma attains a substantialfraction of its ultimate density. As such, reliability of ignition andgrowth of the plasma can be accelerated and improved.

In some embodiments, to reduce heat buildup in the ultraviolet lightsource 160, the ultraviolet light source 160 can be pulsed with multiplerapid pulses at very short intervals (e.g., less than 10 milliseconds).The ultraviolet light source 160 can start pulsing prior to or justfollowing the time of initiation of RF power 134 supplied to theinductively coupled source 135. In some embodiments, the ultravioletradiation pulses can have a frequency of at least about 300 per secondso that multiple pulses can contribute ultraviolet photons to anignition process. As such, in some embodiments ultraviolet assistedplasma ignition can only take about 20 milliseconds or less.

In some embodiments, ultraviolet radiation from the ultraviolet lightsource 160 can promote plasma ignition and growth by ejectingphoto-electrons from an irradiated surface(s) 174 proximate the chamberinterior that can include the plasma region 602 as the RF power 134 isapplied to the inductively coupled plasma source 135, as furtherdescribed below.

In some embodiments (not shown in FIG. 6), the plasma processingapparatus 600 can include a controller that controls the ultravioletlight source 160 to emit the ultraviolet light beam. The controller(e.g., a computer, microcontroller(s), other control device(s), etc.)can include one or more processors and one or more memory devices. Theone or more memory devices can store computer-readable instructions thatwhen executed by the one or more processors cause the one or moreprocessors to perform operations, such as turning on the ultravioletlight source to emit the ultraviolet light beam to impinge on a metalsurface or a dielectric surface prior to or during ignition of a plasma,or other suitable operation.

The UV emission assembly 162 includes one or more walls 166, one or morereflective elements (e.g., mirrors) 168 and a vacuum window 172. Thewall(s) 166 is grounded. At least a portion of the top structure 162 canbe metal, and/or dielectric. When the ultraviolet light beam 164 isincident on a surface 174 (e.g., a metal surface or a dielectricsurface) at a location proximate the volume that will contain plasma,the surface 174 can emit one or more electrons into that region 602. Insome embodiments, an instantaneous output power of ultraviolet radiationfrom the light source 160 at the time of plasma ignition can be about 10milliwatts and more preferably 0.1 Watt or more. UV radiation isemployed because the photo-emission of an electron from an insulatorrequires such photon energy that it can raise a valence electron pastthe conduction band and into the free electron energy space. Forphotoemission from metal, photon energy from the ultraviolet lightsource 160 can raise an electron from a conduction band to a free state.In some embodiments, the photo-electron emission from the surface 174 ofthe UV emission assembly 162 can include at least 100 electrons.

In some embodiments, electrons emitted from the surface 174 can then beaccelerated by electrical fields in the plasma region 602 to causeionization of the gas in the interior of the chamber 120 where plasmawill be located. The ionization can then provide additional electronsthat take part in exponential growth “avalanche” of ionization andresultant electron density, which forms the plasma. In some embodiments(not shown in FIG. 6), a plasma-facing surface irradiated withultraviolet radiation can be a part of a dielectric wall of a plasmachamber, as further described in FIG. 3. The dielectric wall can havesubstantial electric fields when an RF power is being provided to aninductive coupling antenna. In some embodiments (not shown in FIG. 6),ultraviolet irradiated surface can be a metal surface on an interior ofa plasma chamber that has a line of sight to a region of the chamberinterior that will contain plasma, as further described in FIG. 4.

As can be seen in FIG. 6, the ultraviolet light beam 164 is reflectedonto the surface 174 via a reflective element (e.g., a mirror) 168.Electrons 176 emitted from the surface 174 directly into the region 602that will contain plasma.

The vacuum window 172 separates the UV source 160 from the plasmachamber interior 125. The vacuum window 172 can be an ultraviolettransmissive window. For instance, the window 172 can have at least oneof: synthetic quartz, UV-grade sapphire, magnesium fluoride (MgF2)material, or calcium fluoride (CaF2) material. As another example, aspace between the ultraviolet light source(s) and the window can befilled with a gas (e.g., helium or nitrogen) to reduce UV absorption byatmospheric oxygen.

In some embodiments (not shown in FIG. 6), the UV emission assembly canbe a sealed chamber having at least two electrodes and a high-pressureinert gas such as xenon. The vacuum window can in part be made of a UVtransmissive material such as synthetic quartz. Ignition of plasma canbe facilitated by supplying appropriate RF power to the inductivecoupling antenna at the same time as supplying pulsed DC power to theelectrodes in the UV emission assembly such that that the UV emissionassembly can produce copious UV radiation that illuminates dielectricwall(s) and/or metal wall(s) of the plasma chamber.

While the present subject matter has been described in detail withrespect to specific example embodiments thereof, it will be appreciatedthat those skilled in the art, upon attaining an understanding of theforegoing may readily produce alterations to, variations of, andequivalents to such embodiments. Accordingly, the scope of the presentdisclosure is by way of example rather than by way of limitation, andthe subject disclosure does not preclude inclusion of suchmodifications, variations and/or additions to the present subject matteras would be readily apparent to one of ordinary skill in the art.

What is claimed is:
 1. A plasma processing apparatus, comprising: aplasma chamber; a dielectric wall forming at least a portion of theplasma chamber; an inductive coupling element located proximate thedielectric wall; an ultraviolet light source configured to emit anultraviolet light beam onto a metal surface that faces an interiorvolume of the plasma chamber; and a controller configured to control theultraviolet light source.
 2. The plasma processing apparatus of claim 1,further comprising one or more reflective elements configured to reflectthe ultraviolet light beam onto the metal surface.
 3. The plasmaprocessing apparatus of claim 1, wherein the metal surface iselectrically grounded.
 4. The plasma processing apparatus of claim 1,wherein the ultraviolet light source emits the ultraviolet light beamhaving energy in a wavelength range of about 100 nanometers to about 250nanometers.
 5. The plasma processing apparatus of claim 1, furthercomprising an electrostatic shield located between the dielectric walland the inductive coupling element.
 6. The plasma processing apparatusof claim 1, wherein the ultraviolet light beam passes through a windowto reach the metal surface, wherein the window is at least partiallytransparent to the ultraviolet light beam.
 7. The plasma processingapparatus of claim 6, wherein the window comprises at least one of:synthetic quartz, UV-grade sapphire, magnesium fluoride (MgF₂) material,or calcium fluoride (CaF₂) material.
 8. The plasma processing apparatusof claim 6, wherein a space between the ultraviolet light source and thewindow is filled with an inert gas to reduce absorption by atmosphericoxygen, the inert gas comprising at least one of: helium, argon ornitrogen.
 9. The plasma processing apparatus of claim 1, wherein theultraviolet light source emits the ultraviolet light beam onto the metalsurface from a location outside the plasma chamber.
 10. The plasmaprocessing apparatus of claim 1, wherein the ultraviolet light source isa pulsed lamp.
 11. The plasma processing apparatus of claim 1, whereinthe ultraviolet light source comprises at least one of: a xenon arcflashlamp, deuterium lamp, or an excimer RF/pulse xenon lamp.
 12. Theplasma processing apparatus of claim 10, wherein the pulsed lampproduces a plurality of pulses with a frequency of at least about 100per second such that the plurality of pulses contributes ultravioletphotons to be incident on the metal surface.
 13. The plasma processingapparatus of claim 1, wherein the plasma chamber is separated from aprocessing chamber having a workpiece support configured to support aworkpiece.
 14. A method for igniting a plasma in a plasma processingapparatus for semiconducting wafers, comprising: admitting a process gasinto a plasma chamber; emitting an ultraviolet light beam from anultraviolet light source, through a UV transmissive window comprising atleast one of synthetic quartz, sapphire, magnesium fluoride, and calciumfluoride onto a metal surface facing an interior volume of the plasmachamber and energizing an inductive coupling element with a radiofrequency (RF) energy to ignite the plasma in the process gas.
 15. Themethod of claim 14, wherein the ultraviolet light beam is reflected byone or more reflective elements to be incident onto the metal surface.16. The method of claim 14, wherein the metal surface is electricallygrounded.
 17. The method of claim 14, wherein the ultraviolet light beamhas at least 10% of its electromagnetic radiation output in a wavelengthrange of about 100 nanometers to about 250 nanometers.
 18. The method ofclaim 14, wherein the ultraviolet light beam is initiated no later thanabout 10 milliseconds following energizing of the inductive couplingelement.
 19. The method of claim 14, wherein the ultraviolet lightsource emits the ultraviolet light beam onto the metal surface from alocation outside of the plasma chamber.
 20. A plasma processingapparatus, comprising: a plasma chamber; a processing chamber having aworkpiece support configured to support a workpiece; a separation gridseparating the processing chamber from the plasma chamber; a dielectricwall forming at least a portion of the plasma chamber; an inductivecoupling element located proximate the dielectric wall, the inductivecoupling element configured to initiate ignition of a plasma in aprocess gas; an electrostatic shield located between the dielectric walland the inductive coupling element; an ultraviolet light sourceconfigured to emit an ultraviolet light beam onto a metal wall at alocation facing an interior of the chamber; and a controller configuredto control the ultraviolet light source to emit the ultraviolet lightbeam to impinge on the metal wall prior to or at the same time asenergizing the inductive coupling element with radio frequency (RF)energy.
 21. The plasma processing apparatus of claim 20, wherein theultraviolet light beam passes through a window to reach the metal wall,wherein the window is at least partially transparent to the ultravioletlight beam.
 22. The plasma processing apparatus of claim 21, wherein thewindow comprises at least one of: synthetic quartz, UV-grade sapphire,magnesium fluoride (MgF₂) material, or calcium fluoride (CaF₂) material.23. The plasma processing apparatus of claim 21, wherein the window islocated on between the ultraviolet light source and the metal wall. 24.The plasma processing apparatus of claim 22, wherein a space between theultraviolet light source and the window is filled with an inert gas toreduce absorption by atmospheric oxygen, the inert gas comprising atleast one of: helium, argon, or nitrogen.